DC arc plasma from Ti, Al, and Ti 1-x Al x (x ¼ 0.16, 0.25, 0.50, and 0.70) compound cathodes was characterized with respect to plasma chemistry and charge-state-resolved ion energy. Scanning electron microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy of the deposited films and the cathode surfaces were used for exploring the correlation between cathode-, plasma-, and film composition. Experimental work was performed at a base pressure of 10 À6 Torr, to exclude plasma-gas interaction. The plasma ion composition showed a reduction of Al of approximately 5 at. % compared to the cathode composition, while deposited films were in accordance with the cathode stoichiometry. This may be explained by presence of neutrals in the plasma/vapour phase. The average ion charge states (Ti ¼ 2.2, Al ¼ 1.65) were consistent with reference data for elemental cathodes, and approximately independent on the cathode composition. On the contrary, the width of the ion energy distributions (IEDs) were drastically reduced when comparing the elemental Ti and Al cathodes with Ti 0.5 Al 0.5 , going from $150 and $175 eV to $100 and $75 eV for Ti and Al ions, respectively. This may be explained by a reduction in electron temperature, commonly associated with the high energy tail of the IED. The average Ti and Al ion energies ranged between $50 and $61 eV, and $30 and $50 eV, respectively, for different cathode compositions. The attained energy trends were explained by the velocity rule for compound cathodes, which states that the most likely velocities of ions of different mass are equal. Hence, compared to elemental cathodes, the faster Al ions will be decelerated, and the slower Ti ions will be accelerated when originating from compound cathodes. The intensity of the macroparticle generation and thickness of the deposited films were also found to be dependent on the cathode composition. The presented results may be of importance for choice of cathodes for thin film depositions involving compound cathodes. V C 2014 AIP Publishing LLC.

Arc plasma from Ti-C, Ti-Al, and Ti-Si cathodes was characterized with respect to charge-stateresolved ion energy. The evaluated peak velocities of different ion species in plasma generated from a compound cathode were found to be equal and independent on ion mass. Therefore, measured difference in kinetic energies can be inferred from the difference in ion mass, with no dependence on ion charge state. The latter is consistent with previous work. These findings can be explained by plasma quasineutrality, ion acceleration by pressure gradients, and electron-ion coupling. Increasing the C concentration in Ti-C cathodes resulted in increasing average and peak ion energies for all ion species. This effect can be explained by the "cohesive energy rule," where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1.37, 1.42, and 1.55 (10 4

We have studied the utilization of TiB2 cathodes for thin film deposition in a DC vacuum arc system. We present a route for attaining a stable, reproducible, and fully ionized plasma flux of Ti and B by removal of the external magnetic field, which leads to dissipation of the vacuum arc discharge and an increased active surface area of the cathode. Applying a magnetic field resulted in instability and cracking, consistent with the previous reports. Plasma analysis shows average energies of 115 and 26 eV, average ion charge states of 2.1 and 1.1 for Ti and B, respectively, and a plasma ion composition of approximately 50% Ti and 50% B. This is consistent with measured resulting film composition from X-ray photoelectron spectroscopy, suggesting a negligible contribution of neutrals and macroparticles to the film growth. Also, despite the observations of macroparticle generation, the film surface is very smooth. These results are of importance for the utilization of cathodic arc as a method for synthesis of metal borides. (C) 2015 AIP Publishing LLC.

Funding Agencies|European Research Council under the European Community Seventh Framework Program (FP7)/ERC [258509]; Swedish Research Council (VR) [642-2013-8020]; Knut and Alice Wallenberg Foundation; SSF synergy grant FUNCASE

Magnetron sputter-deposited TiBx films grown from TiB2 targets are typically highly overstoichiometric with x ranging from 3.5 to 2.4 due to differences in Ti and B preferential ejection angles and gas-phase scattering during transport between the target and the substrate. The authors show that the use of highly magnetically unbalanced magnetron sputtering leads to selective ionization of sputter-ejected Ti atoms which are steered via an external magnetic field to the film, thus establishing control of the B/Ti ratio with the ability to obtain stoichiometric TiB2 films over a wide range in Ar sputtering pressures.

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Arc plasma from Ti-Si compound cathodes with up to 25 at. % Si was characterized in a DC arc system with respect to chemistry and charge-state-resolved ion energy. The plasma ion composition showed a lower Si content, diverging up to 12 at. % compared to the cathode composition, yet concurrently deposited films were in accordance with the cathode stoichiometry. Significant contribution to film growth from neutrals is inferred besides ions, since the contribution from macroparticles, estimated by scanning electron microscopy, cannot alone account for the compositional difference between cathode, plasma, and film. The average ion charge states for Ti and Si were higher than reference data for elemental cathodes. This result is likely related to TiSix phases of higher cohesive energies in the compound cathodes and higher effective electron temperature in plasma formation. The ion energy distributions extended up to ∼200 and ∼130 eV for Ti and Si, respectively, with corresponding average energies of ∼60 and ∼30 eV. These averages were, however, not dependent on Si content in the cathode, except for 25 at. % Si where the average energies were increased up to 72 eV for Ti and 47 eV for Si

We use energy-and time-dependent mass spectrometry to analyze the evolution of metaland gas-ion fluxes incident at the substrate during high-power pulsed magnetron sputtering (HiPIMS) of Groups IVb and VIb transition-metal (TM) targets in Ar. For all TMs, the time-and energy-integrated metal/gas-ion ratio at the substrate plane + / + increases with increasing peak target current density JT,peak due to rarefaction. In addition, + / + exhibits a strong dependence on metal/gas-atom mass ratio ⁄ and varies from ∼1 for Ti (⁄ = 1.20) to ∼100 for W (⁄ = 4.60), with JT,peak maintained constant at 1 A/cm 2. Time-resolved IEDFs confirm that the degree of rarefaction scales with ⁄ : for heavier TMs, the original sputteredatom Sigmund-Thompson energy distributions are preserved long after the HiPIMS pulse, which is in distinct contrast to lighter metals for which the energy distributions collapse into a narrow thermalized peak. Hence, precise timing of synchronous substrate-bias pulses, applied in order to reduce film stress while increasing densification, is critical for metal/gas combinations with ⁄ near unity, while with ⁄ ≫ 1, the width of the synchronous bias pulse is essentially controlled by the metal-ion time of flight. The good agreement between results obtained in an industrial system employing 440 cm 2 cathodes and a laboratory-scale system with a 20 cm 2 target is indicative of the fundamental nature of the phenomena.